Can I delete Aurora 3 User ( rds_superuser_role, AWS_COMPREHEND_ACCESS, AWS_LAMBDA_ACCESS, AWS_LOAD_S3_ACCESS, AWS_SAGEMAKER_ACCESS, AWS_SELECT_S3_ACCESS)

The straightforward answer would be no. These are the default roles created during instance creation and their functionalities are as follows :

AWS_COMPREHEND_ACCESS - Aurora internal maintenance usage

AWS_LAMBDA_ACCESS - Aurora MySQL call lambda function

AWS_LOAD_S3_ACCESS - Upload to S3 bucket

AWS_SAGEMAKER_ACCESS - Aurora internal maintenance usage

AWS_SELECT_S3_ACCESS - Downloading from S3 bucket

rds_superuser_role - superuser role

Hence, these are the default roles, except 'rds_superuser_role', any other roles cannot be deleted. But, I would recommend you to keep the 'rds_superuser_role' role as untouched. An attempt of deleting other roles will result into below error :

ERROR 1396 (HY000): Operation DROP USER failed

You can also confirm all these default roles on instance creation using the SQL command,

SELECT * FROM mysql.role_edges\G

I hope I have answered all your queries.